PlayStation 3 gamers who play Street Fighter X Tekken can team up on the same machine and co-op against other people online. Capcom states that the Xbox 360 won't have that privilege - all four players must be online or offline.
According to Capcom Unity community manager Christian Svensson, the feature can't be patched onto the 360 version, and the mention of the feature in the manual was a mistake.
Svensson stated, “The reason for this difference is because of the architecture differences between gamertags and PSN IDs. I’m not sure of the technical details, but basically it amounts to: Sony made it so you can mix and match online and offline, and Microsoft made it so you can’t.”
Of course, anyone who's played Rock Band on the Xbox 360 would find that statement curious, since players do it all the time. The game merely makes numbered dummy gamertags for each additional person (such as PLAYER, PLAYER1, etc.) In addition, Mortal Kombat allows local players to engage in online play as well.
Perhaps sensing the oddity of Capcom's explanation, Svensson promised, "I'm still digging into this explanation. I'm also confused by it."